Polarization of planar bodies, in particular bodies comprised of piezoelectric and pyroelectric materials, collectively referred to as a ferroelectric material or body, is useful for producing sensors capable of detecting applied forces or differentials in temperature. Techniques for producing polarization patterns in such bodies are well known.
It is known that when a piezoelectric material is stressed or strained, it develops a charge on the surface of the material. When electrodes are placed on opposing surfaces of the piezoelectric material, the induced charge will be distributed over the area of the electrodes, and a voltage potential difference will be induced across the opposing electroded surfaces of the material. The magnitude of the induced voltage across the electroded surface will be proportional to the induced stress across the film's thickness. This signal will slowly decay with time as the stress distribution across the film's thickness comes to equilibrium.
Similarly, it is known that when a pyroelectric material is heated it develops a charge on the surfaces of the material. When electrodes are placed on opposing surfaces of the material, the induced charge will be distributed over the area of the electrodes and a voltage potential difference will be induced across the opposing electroded surfaces of the pyroelectric material. The magnitude of the induced voltage across the electrode surface will be proportional to the change in temperature of the film structure. This signal will slowly decay with time as the temperature across the film's thickness comes to equilibrium.
In order to utilize the piezoelectric or pyroelectric properties of certain materials in a force or temperature sensing application, it is necessary to first polarize the material in a desired configuration. In a variety of applications, it is desired to alternate the polarization over the surfaces of the material. Alternating the polarity of piezoelectric and/or pyroelectric activity at different regions of the sensor surface is highly desirable since this enables, among others, the minimization of induced noise from large area environmental disturbances such as sunlight and wind. Surface acoustic wave (SAW) devices involve longitudinal poling where the direction of polarization is parallel to the surface of the body. While numerous techniques for providing alternating poled regions are known, in general such methods and apparatus involve use electroded films. If polarization through the thickness of the body is to be produced, it generally involves use of an electroded body involving an extra step in which electrodes are deposited on the body surface prior to the polarization process. It is therefore desirable to provide a method and apparatus for providing alternating polarization through the thickness of the body and preferably one that does not require pre-electroded materials.